1. Field of the Invention
The present invention relates to an ink jet recording apparatus configured to discharge ink onto a recording medium to perform recording.
2. Description of the Related Art
A thermal ink jet recording apparatus repeats an operation for scanning a recording medium such as paper with a recording head having a discharge port for discharging ink, and a conveying operation for conveying the recording medium in a direction crossing a direction in which scan is performed with the recording head, to form an image. Thermal energy generated by an energy generation element (hereinafter, also referred to as a heater) provided so as to correspond to the discharge port causes film boiling of the ink. The ink is discharged from the discharge port by pressure of air bubbles produced in this case, and thereby the ink impacts on the recording medium.
It is known that the discharge amount of the discharged ink varies depending on the temperature of the recording head because viscosity and surface tension of the ink used for a recording operation vary with a temperature. Specifically, following phenomenon arises. In the phenomenon, when the temperature of the recording head rises, the discharge amount of the ink increases, and conversely, when the temperature of the recording head decreases, the discharge amount of the ink decreases.
When the variations in the discharge amount of the ink are caused, density unevenness is caused on the recording medium to reduce image quality. Therefore, a technique is used, which performs drive pulse width control for controlling a pulse width of a drive pulse (double pulse) including a prepulse and a main pulse supplied to the energy generation element to keep the discharge amount of the ink in a constant range. The prepulse supplies energy to the ink to a degree that the ink does not foam, to preparatorily heat the ink. The main pulse supplies energy to the ink to a degree that the ink foams. The prepulse and the main pulse are continuously applied, and thereby a droplet of the ink is discharged.
Japanese Patent Application Laid-Open No. 5-31905 discusses the following method. The method reads fluctuation of a temperature of a recording head by means of a temperature sensor, selects a drive pulse based on the temperature of the recording head from a drive pulse table storing a plurality of drive pulses, and sets the discharge amount of ink to a constant range. The drive pulse table stores the drive pulses in which pulse widths of prepulses are mutually different, of a double pulse applied to an energy generation element. A prepulse with a narrower pulse width is selected as the temperature of the recording head rises. All the pulse widths of the prepulses in a conventional technique such as Japanese Patent Application Laid-Open No. 5-31905 are set to a range in which the ink does not foam even when the recording head is in any condition.
A range in which the temperature of the recording head fluctuates during the recording operation can be extended along with recent speedup of recording and high density of the discharge port of the recording head. Thereby, it is required to extend a temperature range of temperature ranges T0 to TL of a head in which discharge amount control can be performed by pulse width modulation. Therefore, use of the drive pulse table including the drive pulse of the prepulse which is not used in Japanese Patent Application Laid-Open No. 5-31905 is considered.
However, an energy amount of a boundary at which the foaming of the ink is started easily fluctuates under the influence of the fluctuation of the temperature of the recording head and the fluctuation with time of the discharge characteristic of the recording head, or the like. Therefore, there is concern that when the prepulse is applied, a liquid minutely foams (a state immediately before the film boiling) depending on the state of the recording head during the recording operation. If the main pulse is applied onto the energy generation element before the air bubbles produced by minute foams are defoamed, normal film boiling does not generated when the main pulse is applied under the influence of the air bubbles, so that the discharge of the ink becomes unstable.